As you rightly say, "successive refinement is a good thing for people to learn". The book's about learning to "think like a physicist" (page 3 :-) - with the idea that the style of thinking will help people pass physics - and also help with problem solving in real world situations. (Of course, physicists do not have a monopoly on this problem solving / thinking style, but in this book it's being applied to physics.)

In response to the specific criticisms:

* I hope that the kilograms-force issue is dealt with in chapter 11, pages 438-446, and throughout the rest of the book, especially chapter 17 (e.g. pages 664-672).

The order of introducing momentum first (chapter 10), then writing Newton's 2nd Law as Fnet = delta(mv)/delta(t) was very deliberate. First of all because it allows a learner to see and work out the connections between momentum, force and impulse, without doing the typical "student memorisation" thing of treating them as three separate, unrelated equations to be stabbed at. And secondly, because it avoids writing down "F = ma" with no context, which I think is the main source of the "kilograms-force" sloppy thinking you mention.

I would hope that the memory of working on the phoney "weight loss" machine in chapter 11, plus the reinforcement of mass vs weight vs force when designing the space station in chapter 17, would prevent a learner from making this kind of error.

* I agree that mentioning guard digits would have been nice. Practically speaking, with a book of finite size, it was difficult to decide what to include in depth, what to mention in passing and what to leave out.

For guidance, I used the AP student performance reviews (which include typical student errors on actual exam questions) and AP scoring guidelines. The scoring guidelines say: "Numerical answers that differ from the published answer due to differences in rounding throughout the question typically receive full credit." Guard digits were never mentioned as typical errors in the student performance reviews - though items such as too many significant digits, units mistakes and algebra mistakes made regular appearances year after year, which is why these topics received proportionally more time than they would in a typical physics book.

* I'd hope that the memory of trying to extrapolate the curved graph on pages 219-221, and discovering that this doesn't work, then extensive exposure to displacement-time graphs for objects with constant acceleration, would make someone think twice before assuming that everything would be a straight line graph. I agree that looking for changes in behaviour or boundary conditions is a useful skill - and one that could be covered when doing something like charging a capacitor. I can just see Frank now, encouraging the learner to extrapolate that graph, with a "do you think this is sensible" component to the question, and a girl in denim when you turn the page, having worked out that it doesn't make sense to do it that way.

* Sorry about the typos - these should be fixed in a reprint.

Oh, and the cannon-firing hazard is (maybe) the reason that stickmen are the stars in that chapter. :-)